Soil remediation is well established as a procedure for complying with environmental clean-up requirements. Continued accumulations of volatilizable organic pollutants in the soil around chemical plants, petroleum plants, manufacturing plants, gasoline filling stations, and agricultural chemical deposits (e.g., pesticides, herbicides, fungicides, etc.) may be considered as a threat to surface water and ground water or a threat to one or more other circumstance which is regulated by environmental laws and rules. Where contaminated soil is objectionable, there are numerous regulations to be considered.
The present invention is concerned with contaminated soil remediation where the volatilizable organic content of the soil exceeds the allowable regulatory maxima but is preferably less than about five weight percent of the soil and more particularly less than about two weight percent of the soil. Examples of suitable soils include solids such as topsoil, river sediments, bedrock, alluvium, and particulate fill materials such as cinders, gravel and slag.
Several procedures for remediating contaminated soils are shown in U.S. Pat. Nos. 4,738,206; 4,974,528; 5,072,674; 5,103,578; 5,121,699; 5,142,998; 5,152,233; 5,187,131; (heat supply for devolatilization by heated flight conveyor) U.S. Pat. Nos. 4,738,206; 5,072,674; 5,142,998; (indirect heating means, e.g. electric heaters or heat exchange fluids) U.S. Pat. No. 5,103,578; and (fuel oil or fuel gas combustion) U.S. Pat. Nos. 4,974,528; 5,121,699; 5,152,233.
None of the prior art processes employ superheated steam in gas/solids contact with the contaminated soil in a system wherein superheated steam and the volatilized and/or volatilizable organic pollutants recirculate with the system at temperatures which maintain the superheated system in a superheated state, i.e., wherein the steam is maintained above its saturation temperature at all times.